Cyclone Marcia: 'going to be a calamity'

Cyclone Lam crossed the Northern Territory coast about 20 kilometres east of the town of Milingimbi as a category 4 cyclone overnight, knocking out two wind monitors in the process. It has been downgraded to a category 3 as the storm moves inland.

About 2000 kilometres to the south-east, Cyclone Marcia has now crossed the coast near Yeppoon, close to Rockhampton, on the central Queensland coast. The storm was rated as a category 5 cyclone, the highest ranking.

Cyclone Marcia was downgraded to category 4 by the Bureau of Meteorology at its 11am briefing.

While twin cyclones reaching Australia are uncommon, Friday's combination may be the first involving storms of category 3 or higher, said Phil Perkins, a meteorologist with the Bureau of Meteorology in Darwin.

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"It's the first time that we have seen two severe cyclones occurring at the same time," Mr Perkins said.

Category 3 storms have sustained wind speeds of 118-159 km/h, with peak gusts of 165-224 km/h, according to the bureau's definitions.

Cyclone Lam knocked out a wind station at Elcho Island late on Thursday, with 150km/h winds the highest recorded at the site. A second station at Milingimbi also halted operations, recording winds at 93km/h at the time.

Wind speeds reached 260km/h at their peak, with sustained winds of 175-185km/h, Mr Perkins said. A storm surge has reached all parts of the Gulf of Carpentaria, with some areas recording seas more than one metre above the astronomical highs, he said.

Weatherzone: NSW radar

Cyclone Marcia, meanwhile, has recorded wind speeds of as much as 285km/h, with sustained winds of 205km/h, Mr Perkins said.

The cyclones are the first to make landfall on mainland Australia this season, the third latest arrival in the past 50 years, the bureau said this week.